Accretion and Collisional Evolution of Our Solar System · 2015-07-13 · Sampling Ancient Mars (SAM) Early solar system bombardment, which created impact-cratered . highlands on

Accretion and Collisional Evolution of Our Solar System

David A. Kring

Lunar and Planetary Institute

Formation of Stars & Planetary Systems

Key environment: Molecular Clouds Key environmental component: Molecular Cloud Cores

Molecular Clouds

Interstellar clouds of dust and gas Temperatures ~ 10 K At these cold temperatures, atoms combine to form molecules (hence, the name molecular cloud). Over 70 molecules have been identified using spectroscopic techniques, including:

Molecular hydrogen H2 Hydrogen cyanide HCN Water H2O Ammonia NH3 Formaldehyde CH2O

Molecular Cloud Cores

Denser regions of dust and gas within molecular clouds Temperatures ~ 10 to 100 K Cores become gravitationally unstable and collapse Dust and gas collapse into a rotating disk rather than a denser sphere, because the cloud core was rotating prior to collapse Disk is generally called a protostellar nebula; in our case, the solar nebula

Hood and Kring (1996)

Protosolar Neighborhood

Isotopes and stardust suggest the Solar System formed in a seething cauldron of interstellar debris with explosive out-bursts of novae, supernovae, and Wolf-Rayet stars. Novae and Wolf-Rayet stars, for example, eject shells of dust and gas with speeds of 1000’s km/s.

National Geographic (1986)

Solar Nebula Processes 105 – 106 years

Planetesimal Accretion 10 Myr

Terrestrial Planet Accretion 100 Myr

National Geographic (1986)

0 10 50

Time (Millions of Years)

CAI Formation 4.5672 ± 0.0006 Ga (e.g., Amelin et al., 2002)

Condensation and/or distillation in solar nebula to produce objects with high concentrations of refractory elements like Ca, Al, Ti, and Pt. Also called refractory inclusions.

Kring

Allende CV3

0 10 50


Chondrule Formation

High-temperature storms in solar nebula melt aggregates of dust, producing a rain of molten silicate and metal droplets that solidify within ~1 hour. Composed dominantly of olivine and pyroxene, although some have Ca,Al-rich compositions that mimic CAI.

0 – 4 Myr (e.g., Hutcheon et al., 1994; Amelin et al., 2002, 2004)

0.1 to 1 mm spherules

Semarkona

Mokoia

Kring

Kring

0 – 7 Myr (e.g., Hutcheon & Phinney, 1996; Brearley et al., 2001; Hua et al., 2002)

0 10 50


Accretion & Aqueous Alteration of Carbonaceous Chondrite Parent Bodies

CAI, chondrules, and Fe,Mg,Si-rich matrix accrete to produce primitive parent bodies. Water and other volatiles were mobilized, altering material in some of these planetesimals.

Allende

Kring

0 10 50


Thermal Metamorphism of Ordinary Chondrite Parent Bodies

Chondrules, and much less CAI and Fe,Mg,Si-rich matrix, accrete to produce primitive parent bodies. Sufficient heating (perhaps by 26Al) thermally meta- morphoses the material, causing recrystallization and chemical equilibrium.

Begins <5 Myr; extends for ~10 Myr (e.g., Gopel et al., 1989) ? ?

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Vesta Differentiates 2.4 ± 0.9 Myr (Lugmair & Shukolyukov, 1998)

A large planetesimal, between the orbits of Mars and Jupiter, melts and differentiates. Meteoritic remnants of this planetesimal include the HED meteorites, which have been tentatively linked to asteroid 4 Vesta.

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Accretion of large terrestrial planets or proto-planets that might still be affected by a late collision or accretional veneer.

Mars Accretes ~14 Myr (Kleine et al., 2002) Mars Core Formation ~2 or ~20 Myr (Kleine & Halliday, 2006) K

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Earth Accretes ≤33 Myr (e.g., Kleine et al., 2002) possibly ~10 - 15 Myr (e.g., Kleine & Halliday, 2006)

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Moon-forming Impact ~50 Myr, although possibly as early as 30 Myr (e.g., Kleine & Halliday, 2006) K

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Within 100 Myr: Nebular Processes Planetesimal and Planetary Accretion Thermal Metamorphism and Differentiation Crust Formation (at least on Moon and Mars)

Kring (2003)

Kring (2003)

65015,151 width = 2.1 mm Impact Melt Breccia Thin-section view, crossed nicols

Nectarian and Early Imbrian Impact Basins

Impact Basin Diameter (km) Age (Ga)

Orientale 930 3.82 – 3.84 ? Schrodinger 320 Imbrium 1,200 3.85 ± 0.01 Bailly 300 Sikorsky-Rittenhouse 310 Hertzprung 570 3.89 ± 0.009 Serenitatis 740 3.895 ± 0.017 Crisium 1,060 3.89 ? Humorum 820 Humboldtianum 700 Medeleev 330 Korolev 440 Moscovienese 445 Mendel-Rydberg 630 Nectaris 860 3.89 – 3.91 ?

For comparison, Chicxulub’s diameter is ~180 km

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implying ~70 to 90 million year bombardment

The Apollo Legacy– The radiometric ages of rocks from the lunar highlands indicated the lunar crust had been thermally metamorphosed ~3.9 – 4.0 Ga. A large number of impact melts were also generated at the same time. This effect was seen in the Ar-Ar system (Turner et al., 1973) and the U-Pb system (Tera et al., 1974). It was also preserved in the more easily reset Rb-Sr system. (Data summary, left, from Bogard, 1995.) A severe period of bombardment was inferred: the lunar cataclysm hypothesis.

Testing the hypothesis:

Was there really an enhanced impact rate at 3.9-4.0 Ga? New analyses of Apollo samples New analyses of lunar meteorites New analyses of asteroid impact melts Analysis of ALH84001, from ancient crust of Mars Thus far, all data are consistent with hypothesis

What was the dominant source of impacting debris? Asteroids? Comets? Kuiper belt objects? Astrobiological issues being investigated: Did the impacting debris deliver significant water and biogenic elements?

How did the impacting debris affect environments suitable for pre-biotic chemistry and the early evolution of life?

Inner Solar System Cataclysm Hypothesis

The chemical compositions of these meteorites indicate they come from non-Apollo sites.

Data support this model

Duration of bombardment 20 to 200 Ma

Cratered Asteroids

Impact melt breccias (e.g., Kring et al., 1996)

Melt veins in crater floors (e.g., Kring et al., 1999)

Kring

Kring

Kring and Cohen (2002)

Lunar Cataclysm

Inner Solar System

Cataclysm

Kring and Cohen (2002)

Strom, Malhotra, Ito, Yoshida, & Kring (Science 2005)

Geological Fingerprints of the Impactor Population

Size distribution of impact craters in ancient terrains were used to calculated the Size distribution of the impacting objects Indicated asteroids were the dominant source of debris

Strom and Sprague

Apollo 16 Sample 60016,181 Ancient regolith breccia that entrains visible (dark-colored) clasts of impact melt. The melts can be analyzed to determine the ages of impacts Their siderophile contents can be used to identify the type of NEA impactors The sample also contains microscopic fragments of impactor relics

False-color element map of Apollo 16 sample 60016. The image was made using innovative micro-analytical mapping technique to mineralogically fingerprint projectile fragments within lunar samples. The colors denote the distribution and concentration of different elements (white = aluminium, blue = silicon, green = magnesium, yellow = calcium, red = iron, pink = titanium, cyan = potassium). The field of view is ~7 × 9 mm.

An UMMF (tiny green particle)

Joy et al. (2012)

Ancient Surfaces

Young Surfaces

Before the Lunar Cataclysm

Ancient Surfaces

Young Surfaces

After the Lunar Cataclysm

Proximity of the Moon to Earth during the Hadean

LPI (Kring and Blackwell)

How was the composition of the atmosphere altered?

How did impacts affect microbial evolution? How did impacts affect complex life (e.g., at K/T boundary)?

What are the future impact hazards?

What types of biogenic elements were delivered?

Earth’s Water

Although the impact cataclysm was sufficiently large to resurface Earth and other terrestrial planets, it was not dominant source of water on Earth and Mars; it delivered too little material. Water had been delivered during earlier accretion. Yet, it still managed to deliver significant biogenic elements For example:

Delivery of Biogenic Elements

Assuming, for example, average projectile compositions comparable to enstatite chondrites: 3.4 x 1021 g S 9.4 x 1020 g H2O 3.2 x 1020 g C (i.e., 160 times larger than the total land biomass today) Delivered in 20 to 200 Ma or, alternatively, 500 to 600 Ma

Kring’s Impact-Origin of Life Hypothesis (with emphasis on the word “hypothesis”)

Hydrothermally-altered Impact Breccia

Chicxulub, Kring et al. (2004)

Thermophillic Organisms in Hydrothermal Environment

Yellowstone

Farmer (2000)

Modeling indicates complex craters had active hydrothermal systems for 104 to several times 106 years on early Earth and Mars.

Impact-generated Hydrothermal Systems

Systems are extensive (spanning entire diameter of each crater) Systems are long-lived (hundred thousand to a few million years, depending on crater size) Leading us to predict (e.g., Kring, 2000, 2004; Abramov and Kring, 2004): (i) Noachian terrains should have abundant hydrothermal minerals (ii) That the hydrothermal alteration will be associated with impact-cratered terrains; because impact cratering is far more abundant than volcanism during this period, most hydrothermal alteration is impact-derived (iii) And younger terrains should have much less hydrothermal minerals because impact rate dramatically decreased. Prediction confirmed by Mars Express (Pouclet et al., Science, 2005)

But we are still operating in a data poor environment…….

Nectarian and Early Imbrian Impact Basins


Orientale 930 3.82 – 3.84 ? Schrodinger 320 Imbrium 1,200 3.85 ± 0.01 Bailly 300 Sikorsky-Rittenhouse 310 Hertzprung 570 3.89 ± 0.009 Serenitatis 740 3.895 ± 0.017 Crisium 1,060 3.89 ? Humorum 820 Humboldtianum 700 Medeleev 330 Korolev 440 Moscovienese 445 Mendel-Rydberg 630 Nectaris 860 3.89 – 3.91 ?

For comparison, Chicxulub’s diameter is ~180 km

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Pre-Nectarian Basins


Apollo 505 Grimaldi 430 Freundlick-Sharonov 600 Birkhoff 330 Planck 325 Schiller-Zucchius 325 Amundsen-Ganswindt 355 Lorentz 360 Smythii 840 Coulomb-Sarton 530 Keeler-Heaviside 780 Poincare 340 Ingenii 560 Lomonosov-Fleming 620 Nubium 690 Mutus-Vlacq 690 Tranquillitatis 800 Australe 880 Fecunditatis 990 Al-Khwarizmi/King 590 Pingre-Hausen 300 Werner-Airy 500 Balmer-Kapteyn 550 Flamsteed-Billy 570 Marginis 580 Insularum 600 Grissom-White 600 Tsiolkovskiy-Stark 700 South Pole-Aitken 2500 Procellarum 3200

?

Representative Eratothenian Craters

Impact Crater Diameter (km) Age (Ga)

Lambert 30 Reiner 30 Archytas 32 Timocharis 34 Stearns 37 Manilius 39 Herschel 41 Rothmann 42 Plinius 43 Reinhold 43 Agrippa 44 Hainzel A 53 Maunder 55 Eratosthenes 58 Bullialdus 61 Hercules 69 Werner 70 Fabricius 78 Aristoteles 87 Theophilus 100 (rayed) Pythagoras 130 Langrenus 132 (rayed) Hausen 167 (largest young crater)

?

Representative Copernican Craters

Impact Crater Diameter (km) Age (Ga)

Kepler 32 Petavius B 33 Godin 35 Autolycus 39 (ray at A15 site?) 1.29 Aristarchus 40 Olbers A 43 Crookes 49 Anaxagoras 51 Aristillus 55 (ray at A15 site?) 1.29 Taruntius 56 Eudoxus 67 King 77 Tycho 85 (landslide at A17 site?) 0.1 Copernicus 93 (ray at A12 site) 0.8-0.9

The age of only a single impact event, Tycho, is known during the Phanerozoic of Earth, which is the period of complex life on our planet. One cannot determine an impact rate with only a single data point. Were there pulses of activity at, say, 800 and 500 Ma?

Human-assisted sample return mission • In 2021, NASA will fly crew around the Moon in the Orion vehicle.

• In subsequent missions, a robotic rover on the surface could collect samples and launch them into orbit, where astronauts could retrieve them for return to Earth.

Burns, Kring, Norris, Hopkins, Lazio, & Kasper (2013)

David A. Kring

LPI (Kring)

Sampling Ancient Mars (SAM)

Early solar system bombardment, which created impact-cratered highlands on Mars, ejected ancient crustal and potentially mantle components from Mars. Calculations suggest 2 to 10% of the regolith of Diemos is composed of these ancient Mars samples. Albedo measurements of Diemos confirm a bright component occurs in regolith that is consistent with Mars material. SAM can collect ~2 kg of Diemos regolith, which will contain 40 g to perhaps 200 g of Mars samples.

Thank you.

Accretion and Collisional Evolution of Our Solar System · 2015-07-13 · Sampling Ancient Mars (SAM) Early solar system bombardment, which created impact-cratered . highlands on

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